Conventional fuel pumps, such as those used with aircraft engines, are typically configured as positive displacement pumps. Typical positive displacement pumps include a housing defining a fuel pump chamber, an impeller rotatably mounted within the fuel pump chamber, and a drive coupling that attaches the impeller to an associated gear box located inside the engine. During operation, as the engine causes the impeller to rotate, the impeller draws fuel from a fuel tank into an inlet port of the housing and causes the fuel to exit into the engine through a discharge port of the housing.
Conventional fuel pumps can utilize several different types of sealing mechanisms to minimize leakage of fluids between the engine and the fuel pump chamber. For example, certain fuel pumps include a bearing that is operable to limit leakage of oil from the drive side of the fuel pump into the fuel pump chamber. The oil-lubricated bearing is disposed about a shaft of the impeller and within the fuel pump housing between the engine and the fuel pump. An inner surface of the bearing contacts the shaft of the impeller. Such contact helps to limit leakage of oil from the engine and the bearing into the fuel pump chamber of the fuel pump.
Other conventional fuel pumps include sealing elements that are operable to limit leakage of fuel from the fuel pump chamber into the engine. For example, certain fuel pumps include concentrically arranged primary and secondary sealing members, disposed between the fuel pump chamber and the engine, configured to form redundant seals with a flat seal face of the impeller (i.e., where the flat seal face of the impeller is substantially perpendicular to the shaft of the impeller). With such a configuration, during operation the primary seal minimizes leakage of fuel from the fuel pump chamber past the impeller and into the engine. In the event that the primary seal fails, the secondary seal becomes pressure loaded against the flat seal face of the impeller face to minimize leakage of fuel from the fuel pump chamber into the engine.